1976 XS650 Starving for Fuel?

Commuter

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I've been working through jetting for pods and pipes, and throughout the process, as well as before, it seems if I run at 70 mph for any length of time, it starves for fuel after a couple minutes. If I slow down or stop, it may die, it starts right back up but from then until I park it, it runs rough, like its running out of gas. I have aftermarket petcocks, they had plastic screens on both the ON standpipes and the RESERVE standpipes. The bike sat from 1997 til a couple months ago with fuel in it, the tank was pretty grungy but I've cleaned it a couple times, the second time because I thought newly loosened up crap had plug up my screens. I replaced the plastic screens with stainless screens that were about 7/16 diameter tubes, I pinched one end, flattened them enough to get them in through the hole in the tank, and pinched them onto the stand pipes (I didn't pinch the standpipes). As usual, my first test ride after that seemed like it was ok, but maybe I didn't go 70 for long enough? Seems like if I run 60, I'm ok, 70 it eventually starves for fuel (I think). It still could be more crap coming from places in the tank I can't see with the bore scope and the chain couldn't get to. I've had the carb bowls off several times changing pilot jets, they look nice and clean. Could the petcocks not deliver enough fuel (seems unlikely there are two of them)? Should I put in an inline filter (I don't see crap in the carb bowl, but I'm kind of curious as to what I may catch)?

Thoughts?
Float heights? floats set a little bit too low can do what you describe. Ignition timing. I once had a bike which I subsequently found had faulty electronic ignition it would start normally fly along and then get slower and slower. The faulty automatic advnce curve which was programmed at the factory was gradually retarding the ignition as the electronic ignition module heated up. It took me ages to trace this issue and the bike was off the road for a very long time until I reverted to points and mechanical advance and discovered all my long lost power.The ignition issue is not normal ... I would look at float heights first. Also do you have one fuel tap or two? even though the carbs are normally linked, people with 2 fual taps can find a quick fix by running the bike with both fuel taps opened up. (my XS650 B has linked fuel supplies and also two fuel taps..it should run with one tap open only)
 

Wilsonsk

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Float heights? floats set a little bit too low can do what you describe. Ignition timing. I once had a bike which I subsequently found had faulty electronic ignition it would start normally fly along and then get slower and slower. The faulty automatic advnce curve which was programmed at the factory was gradually retarding the ignition as the electronic ignition module heated up. It took me ages to trace this issue and the bike was off the road for a very long time until I reverted to points and mechanical advance and discovered all my long lost power.The ignition issue is not normal ... I would look at float heights first. Also do you have one fuel tap or two? even though the carbs are normally linked, people with 2 fual taps can find a quick fix by running the bike with both fuel taps opened up. (my XS650 B has linked fuel supplies and also two fuel taps..it should run with one tap open only)
I think I found my power loss issue, not fuel related at all, it seems. I put new Emgo coils on when I was reviving the bike a month ago or so, I was just refreshing things like that. Looks like it was one of those coils failing when hot. I i put the original coils back in, I have about 50 miles of solid 60-70 mph running on it now, couldn't get 5 miles before. Now I have some charging gremlins.

I have always kept both petcocks open, even with the crossover pipe. These petcocks are not great, they don't shut all of the way off and the handles/standpipes are backwards so handles are up for ON and down for RESERVE. I'd love to here of a source for good petcocks.
 
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Wilsonsk

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I'll check my rotors (1981 and 1976) and report back for runout, ohms and cleanliness/smoothliness.
1981 Rotor - 5.1 ohms, clean shiny slip rings
1976 Rotor - 5.8 ohms, smooth but dingy slip rings

If I take the stator off to clean, should I swap to the 1981 rotor? I'll have my magnet for TCI when the time comes.

Do I need to take the stator off to clean? Hard to see the inner ring, but I could get a piece of 320 in there.
 

gggGary

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1981 Rotor - 5.1 ohms, clean shiny slip rings
1976 Rotor - 5.8 ohms, smooth but dingy slip rings

If I take the stator off to clean, should I swap to the 1981 rotor? I'll have my magnet for TCI when the time comes.

Do I need to take the stator off to clean? Hard to see the inner ring, but I could get a piece of 320 in there.
Stators are rather reliable. But the wire bundle back by the sprocket is a known trouble spot. A number of times we've a found a wire back there hanging on "by a thread", might be worth exploring, cut the sheath and dig down looking for funky insualtion or wires that bend "too easy" somewhere.
 
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Wilsonsk

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Stators are rather reliable. But the wire buyndle back by the sprocket is a known trouble spot. A number of times we've a found a wire back there hanging on "by a thread" might be worth exploring, cut the sheath and dig down looking for funky insualtion or wires that bend "too easy" somewhere.
I cleaned up the left side cover from the 1981 motor, now's probably a good time to swap that, and during that process, go back to my 17 tooth drive sprocket, clean my rotor and check my wire harness.
 

gggGary

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PS the rotor slip rings are thin, I prefer nothing stronger than buffing compound. And don't clean often or ever if the rings are clean and black, a layer of carbon from the brushes improves the connection.
 

Jim

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I'll offer a theory...
At higher rpm's the rotor's gonna see a lot more centrifugal force. These rotors are 40+ yrs old and the insulation (varnish) on the copper wire is breaking down and causing a partial short at higher rpm's. Never actually heard of that happening, but.....
 

jpdevol

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I'll offer a theory...
At higher rpm's the rotor's gonna see a lot more centrifugal force. These rotors are 40+ yrs old and the insulation (varnish) on the copper wire is breaking down and causing a partial short at higher rpm's. Never actually heard of that happening, but.....
It's practically one of the few things that makes sense. Worth changing-out to see if it affects the symptom........👍
 

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I cleaned up the left side cover from the 1981 motor, now's probably a good time to swap that, and during that process, go back to my 17 tooth drive sprocket, clean my rotor and check my wire harness.
Well, my impatience got the better of me, I got the small cover off, determined I could roll up a sheet of 400 grit paper and get it into the inner ring from the top, grabbed an air blower and hit it with that at the same time, as soon as I hit the outer ring with the sand paper the motor slowed, I hit the inner a couple of times, shined them both up. 14.2-14.4, from 1,200 rpm idle to 75 mph, doesn't pull down on acceleration at all now, just doesn't move. Maybe those Emgos aren't "bad"? just draw enough when they heat up to outrun the charging system? I did Jan's battery only test, they did exactly the same thing, interesting, but not funny. I haven't thrown the Emgos away, I was keeping my old ones (now on the bike) for spares, while the Emgos angered and upset me, they did always get me home.
 

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It's practically one of the few things that makes sense. Worth changing-out to see if it affects the symptom........👍
I saw this after my last post, I got impatient and just wanted to try to solve this so I cleaned the slip rings, seems to have resolved it (for now). I have both left and right engine covers cleaned and a little polished (this bike is a survivor, not a beauty queen). I want to do both sides, service the starter gear, change out the rotor, maybe the stator as well so I have the TCI pickup (I know I need to rewire the brushes) and rotor ready to go if I ever do switch ignitions. My comfortable riding season here in East Central Minnesota is getting towards the short end, even these past hot days, once your over 30 mph, the air is chilly. While I was born and raised in this godforsaken ice palace part of this country, I don't like being cold. All of that to say, I want to make as much of the rest of the riding season as I can, then it's 41 Ford season until the snow/salt flies (that has a heater, in addition to poor firewall insulation and a flathead that runs hot, and not performance hot, just heat hot).
 

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PS the rotor slip rings are thin, I prefer nothing stronger than buffing compound. And don't clean often or ever if the rings are clean and black, a layer of carbon from the brushes improves the connection.
I ALSO saw this after the fact, I didn't press hard, I had seen another thread where they said to use 320 lightly, the closest I had was 400. After my run without the battery charging system connected, I plugged in the VR while it was running, I was surprised how much the alternator loaded the engine, I un-plugged and re-plugged it in a few times to confirm it wasn't just a random rpm change. It did that as soon as I shined up the outer ring. I'll find excuses to get out and ride some more tonight and see if it holds.
 

jpdevol

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No problem - understand that consideration. You have an on-board voltmeter, so you're in good shape as the concern is that the lower voltage at high rpm may indicate a rotor perhaps heading south - if it does fail without the voltmeter, you have little warning until it's dead on the berm. You'll get a warning and can head straight to the barn
 

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?
Is the TCI that sensitive on 12-14.5volts?

Sounds like heat or fuel stave.


cliff
If the rotor shorts, it'll suck the battery dead pretty quick. It'd last a bit longer if caught and unplugged.

IME the ignition does ok until available voltage gets below 11VDC, then it breaks-up and eventually quits sparking.
 
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5twins

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I use plain old chrome polish to clean the slip rings, followed by a wipe-down with electrical contact cleaner to remove any polish residue. Yes, I remove the stator, but just swing it off to the side and rest it on some wood blocks. Here's one ring cleaned, the other not .....

Slip Ring Cleaning.jpg


..... and both done .....

Slip Rings Clean.jpg


I know Gary likes to leave them dirty but over the years I've encountered a few bikes that actually quit charging because the rings got too dirty. So, I like to start off on a new-to-me bike with them clean. After that, I can monitor them and let them get dirty again, to a point, then clean them again if need be. But honestly, after my initial clean-up, I haven't needed to re-clean any yet.
 

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Went for another ride, rock solid 14.2-14.4, regardless of load, throttle position, speed, etc.

For the time being, I’ll ride it and keep an eye on things.
 

Wilsonsk

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I use plain old chrome polish to clean the slip rings, followed by a wipe-down with electrical contact cleaner to remove any polish residue. Yes, I remove the stator, but just swing it off to the side and rest it on some wood blocks. Here's one ring cleaned, the other not .....

View attachment 250070

..... and both done .....

View attachment 250071

I know Gary likes to leave them dirty but over the years I've encountered a few bikes that actually quit charging because the rings got too dirty. So, I like to start off on a new-to-me bike with them clean. After that, I can monitor them and let them get dirty again, to a point, then clean them again if need be. But honestly, after my initial clean-up, I haven't needed to re-clean any yet.

Sounds like I got a little aggressive with my slip ring cleaning, but, it seems to have improved things. I’ll warily put some miles on and see how things go.

I really appreciate all of the help!! Thank you!!!
 
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